Allergen-specific serum IgE testing. Measurement of food-specific serum IgE levels is routinely available and requires only a blood specimen. The test can be used in patients with skin disease, and results are not affected by concurrent medications. The presence of food-specific IgE indicates that the patient is sensitized to that allergen and might react upon exposure; children with a higher level of antibody are more likely to react.29
Food-specific serum IgE tests are sensitive but nonspecific for food allergy.31 Broad food-allergy test panels often yield false-positive results that can lead to unnecessary dietary elimination, resulting in years of inconvenience, nutrition problems, and needless health care expense.32
It is appropriate to order tests of specific serum IgE to foods ingested within the 2 to 3–hour window before onset of symptoms to avoid broad food allergy test panels. Like skin-prick testing, positive allergen-specific serum IgE tests alone cannot diagnose food allergy.
Oral food challenge. The double-blind, placebo-controlled oral food challenge is the gold standard for the diagnosis of food allergy. Because this test is time-consuming and technically difficult, single-blind or open food challenges are more common. Oral food challenges should be performed only by a physician or other provider who can identify and treat anaphylaxis.
The oral challenge starts with a very low dose of suspected food allergen, which is gradually increased every 15 to 30 minutes as vital signs are monitored carefully. Patients are observed for an allergic reaction for 1 hour after the final dose.
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